Question: In 21 years, Jessica will be 4 times as old as she is right now. How old is she right now?
Explanation: We can use the given information to write down an equation about Jessica's age. Let Jessica's age be $j$ In 21 years, she will be $j + 21$ years old. At that time, she will also be $4 j$ years old. Writing this information as an equation, we get: $j + 21 = 4 j$ Solving for $j$ , we get: $3 j = 21$ $j = 7$.